Black silicon. Coloured scanning electron micrograph showing the surface structure of black silicon. This is a modified form of silicon whose surface is covered with monocrystalline silicon needles. These needles dramatically increase the substance's surface area and are thought to be responsible for the materials very high light-absorbing properties. Due to this high absorbency black silicon is used in photodetectors and solar cells. Magnification: x100 when printed at 10 centimetres wide.